The present invention relates generally to a structural reinforcement system for use in increasing the stiffness, strength, or durability of different portions of automotive or aerospace vehicles. More particularly, the present invention relates to structurally reinforced closed forms, such as a hydroform structure or hydroform rail, which utilizes an expandable and foamable material to cross-link, structurally adhere, and reinforce the form when the foamable material becomes chemically active and expands upon heating.
Traditionally, closed form or hydroforming techniques are used to draw and shape metal tubes. Conventional hydroforming techniques often involve two steps: (1) placing the desired bends in the tube and (2) forming the tube to the desired configuration. Step 2 of this process usually requires placing a tubular member having an open bore in a mold and pinching off the ends of the tube. A pressurized liquid is then injected into the open bore, causing the tube to stretch and expand out against the mold.
The manufacturing advantages of the hydroforming process is that it allows formation of relatively long tubular structures having a seamless perimeter. This process elminates the cost of welding, machining, or fastening operations often used to shape the part in the desired configuration. As a result, a hydroform or closed form structure very often has a high length to diameter ratio. For instance, a hydroform structure may have a length in excess of 15xe2x80x2 and a diameter ranging from approximately xc2xexe2x80x3 to more than 12xe2x80x3. To this end, a further manufacturing process advantage of a hydroform structure is that it can exceed the length of other tubular members, such as torsion bars or tubular bars, formed using other processes.
Additionally, hydroforming processing creates complex structural shapes that typically include bends and contour changes. Often the number of bends and contour changes in a hydroformed bar are greater and more complex than those found in torsion bars or other tubular structures formed using different techniques.
Hydroform structures typically have a constant wall thickness prior to forming, and might develop strength differences at the site of bends or changes in contour, as well as at certain locations along a long tubular section. Thus, it is often desirable to reinforce closed form and hydroform sections to improve their structural stiffness, strength, and durability, particularly in automotive vehicle applications.
Traditional ways of reinforcing tubular structures such as hydroforms and other closed forms include sliding a metal sleeve inside the tube and welding the reinforcing member in place. However, because the hydroform often includes one or more bends or one or more changes in contour and/or diameter, it is often difficult to insert the sleeve into the hydroform at the precise location of the weak portion. Other techniques include reinforcing the hydroform from the outside by welding the sleeve onto the outside of the hydroform. However, hydroforms are often used in applications having very close tolerances, resulting in little or no clearance for an externally placed reinforcing member. Accordingly, exterior reinforcements are often not as effective as interior reinforcements.
Additionally, in many operations the weight of the tubular member is critical and must be kept low as possible. Thus, the use of an external sleeve adds unwanted weight to the tubular assembly. Still further, the welding operation tends to be labor intensive, time consuming and inexact, increasing the cost of forming the hydroform member and producing parts that have questionable reliability. Finally, these additional manufacturing steps and operations are often cumbersome and difficult to integrate into a final vehicle manufacturing process in that additional tooling would need to be developed by the manufacturer and assembly plant resources, labor, maintenance, and space would need to be dedicated and expensed by the vehicle manufacturer.
Accordingly, there is a need in industry and manufacturing operations for system, device, and method for reinforcing the weak areas of closed forms and other hydroform tubes without significantly increasing the weight and manufacturing complexity. In particular, there is a need for reinforcing a closed form or hydroform, which utilizes a plurality of members or pieces to achieve integrated reinforcement within the closed form since the contour or shape of typical tubes do not allow for placement of single piece reinforcement members. In this regard, the present invention addresses and overcomes the shortcomings found in the prior art by providing a multi-piece reinforcement system having at least two members capable of being nested together within a hydroform that may then be fixed in location through the use of a third member which serves as a locking and positioning member of the reinforcement system within the hydroform or other closed form. However, design of two nesting member could also create a lock mechanism. Structural reinforcement of the hydroform is achieved through activation by heat of an adhesive material disposed along at least two of the members, such a material would typically expand to contact a substrate surface and in doing so structurally adhere the multiple members to each other and the hydroform.
The invention relates to methods and systems for reinforcing a closed form or hydroform member. In one embodiment, the hydroform member includes an outer structural member having an open bore; and an expandable material or structural foam supported by the outer structural member. The expandable material extends along at least a portion of the length of the outer structural member, and may fill at least a portion of the length of the bore.
The expandable material is generally and preferably a heat-activated epoxy-based resin having foamable characteristics upon activation through the use of heat typically encountered in an e-coat or other automotive painting operation. As the foam is heated, it expands, cross-links, and structurally adheres to adjacent surfaces. Preferred structural foam materials are commercially available from LandL Products, Inc. of Romeo, Mich. under the designation L5204, L5206, L5207, L5208, or L5209. Generally speaking, these automotive vehicle applications may utilize technology and processes such as those disclosed in U.S. Pat. Nos. 4,922,596, 4,978,562, 5,124,186, and 5,884,960 and commonly owned, co-pending U.S. patent application Ser. No. 09/502,686 filed Feb. 11, 2000, Ser. No. 09/524,961 filed Mar. 14, 2000, and particularly, Ser. No. 09/459,756 filed Dec. 10, 1999, all of which are expressly incorporated by reference.
The system generally employs two or more members adapted for stiffening the structure to be reinforced and helping to redirect applied loads. In use, the members are inserted into a closed form, such as a hydroformed tube, with the heat activated bonding material serving as the load transferring and potentially energy absorbing medium. In a particularly preferred embodiment, at least two of the composite members are composed of an injection molded nylon carrier, an injection molded polymer, or a molded metal (such as aluminum, magnesium, and titanium, an alloy derived from the metals or a metallic foam derived from these metals or other metal foam) and it is at least partially coated with a bonding material on at least one of its sides, and in some instances on four or more sides. A preferred bonding medium is an epoxy-based resin, such as L5204, L5206, L5207, L5208 or L5209 structural foam commercially available from L and L Products, Inc. of Romeo, Mich. However, the third member which serves to lock and position the first two members could also utilize an adhesive material along its outer surface. In addition, it is contemplated that the member could comprise a nylon or other polymeric material as set forth in commonly owned U.S. Pat. No. 6,103,341, expressly incorporated by reference herein. Still further, the member adapted for stiffening the structure to be reinforced could comprise a stamped and formed cold-rolled steel, a stamped and formed high strength low alloy steel, a stamped and formed transformation induced plasticity (TRIP) steel, a roll formed cold rolled steel, a roll formed high strength low alloy steel, or a roll formed transformation induced plasticity (TRIP) steel. In essence, any material that is considered structural may be used in conjunction with the structural foam. The choice of the structural material used in conjunction with a structural foam or other bonding medium will be dictated by performance requirements and economics of a specific application.
Additional foamable or expandable materials that could be utilized in the present invention include other materials which are suitable as bonding or acoustic media and which may be heat activated foams which generally activate and expand to fill a desired cavity or occupy a desired space or function when exposed to temperatures typically encountered in automotive e-coat curing ovens and other paint operations ovens. Though other heat-activated materials are possible, a preferred heat activated material is an expandable or flowable polymeric formulation, and preferably one that can activate to foam, flow, adhere, or otherwise change states when exposed to the heating operation of a typical automotive assembly painting operation. For example, without limitation, in one embodiment, the polymeric foam is based on ethylene copolymer or terpolymer that may possess an alpha-olefin. As a copolymer or terpolymer, the polymer is composed of two or three different monomers, i.e., small molecules with high chemical reactivity that are capable of linking up with similar molecules. Examples of particularly preferred polymers include ethylene vinyl acetate, EPDM, or a mixture thereof. Without limitation, other examples of preferred foam formulation that are commercially available include polymer-based material commercially available from LandL Products, Inc. of Romeo, Mich., under the designations as L-2105, L-2100, L-7005 or L-2018, L-7101, L7102, L-2411, L-2420, L-4141, etc. and may comprise either open or closed cell polymeric base material.
Further, it is contemplated that if an acoustic material is used in conjunction with the present invention, when activated through the application of heat, it can also assist in the reduction of vibration and noise in the overall automotive body. In this regard, the now reinforced closed form or hydroform will have increased stiffness in the cross-members, which will reduce the natural frequency, measured in hertz that resonates through the automotive chassis and reduced acoustic transmission and the ability to block or absorb noise through the use of the conjunctive acoustic product. By increasing the stiffness and rigidity of the cross-members, the noise and frequency of the overall engine ride vibration that occurs from the operation of the vehicle can be reduced since a reduced frequency of noise and vibration will resonate through the chassis. Although the use of such vibration reducing materials or media can be utilized instead of, or in conjunction with, the structural expandable material, the preferred embodiment of the structural reinforcement system of the present invention utilizes the structurally reinforcing expandable material. Use of acoustic materials in conjunction with structural may provide additional structural improvement but primarily would be incorporated to improve NV H characteristics.
It is also contemplated that foamable or expandable material could be delivered and placed into contact with the member or hydroform, such as hydroform tube found in automotive applications, through a variety of delivery systems which include, but are not limited to, a mechanical snap fit assembly, extrusion techniques commonly known in the art as well as a mini-applicator technique as in accordance with the teachings of commonly owned U.S. Pat. No. 5,358,397 (xe2x80x9cApparatus For Extruding Flowable Materialsxe2x80x9d), hereby expressly incorporated by reference. In this non-limiting embodiment, the material or medium is at least partially coated with heat-activated polymer that could be structural or acoustic in nature. This preferably heat activated material can be snap-fit onto the chosen surface or substrate; placed into beads or pellets for placement along the chosen substrate or member by means of extrusion; placed along the substrate through the use of baffle technology; a die-cutting operation according to teachings that are well known in the art; pumpable application systems which could include the use of a baffle and bladder system; and sprayable applications.
In one embodiment, at least two members composed of an injection molded nylon are provided with a suitable amount of bonding or load transfer medium molded onto its sides in at least one location wherein each portion is smaller in diameter than a corresponding insertable opening in the form or tube to enable placement within a cavity defined within an automotive vehicle, such as portions of a hydroform tube section or other area or substrate found in an automotive vehicle which could benefit from the structural reinforcement characteristics found in the present invention. In this embodiment, a first portion corresponds to, and is insertably attached to an opening located within a lower portion of the hydroform tube section. A second portion is slideably engaged and affixed to an upper surface of the first portion. A third portion is then utilized to fixedly bridge the first and second portions together within the hydroform tube. It is contemplated that the bonding medium could be applied to a substrate in a variety of patterns, shapes, and thicknesses to accommodate the particular size, shape, and dimensions of the cavity corresponding to the chosen form or vehicle application. The expandable material or bonding medium is activated to accomplish expansion through the application of heat typically encountered in an automotive e-coat oven or other painting operation oven in the space defined between the plurality of members and the walls of the hydroform tube defining the cavity. The resulting structure includes the wall structure of the hydroform tube joined to the plurality of members with the aid of the structural foam.